A research program, conducted by Rennselaer Polytechnic Institute for Koppers Co., Inc., on the design and engineering of expanded polystyrenecore (Dylite) panels, proved conclusively prior to test reported here that structurally adequate panels can be designed. As an adjunct to this primary objective, the performance of panels in actual use in a structure exposed to climatic varations was considered to be of equal importance in predicting the long-term behavior and durability of this type of construction. By careful instrumentation, data on the long-term behavior of panels under normal use could be gathered and analyzed. Further, by using panels as load-bearing and non-load-bearing structural members with a variety of face materials, comparative data would be obtained on the relative merits of several common facings.